<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="../../scripts/jquery.js" type="text/javascript"></script>
</head>
<body>
<textarea id="mytextarea"></textarea>

<script>
jQuery.fn.maxLength = function(max){
	this.each(function(){
		var type = this.tagName.toLowerCase();
		var inputType = this.type? this.type.toLowerCase() : null;
		if(type == "input" && inputType == "text" || inputType == "password"){
			//应用标准的maxLength
			this.maxLength = max;
		}else if(type == "textarea"){
			this.onkeypress = function(e){
				var ob = e || event;
				var keyCode = ob.keyCode;
				var hasSelection = document.selection? document.selection.createRange().text.length > 0 : this.selectionStart != this.selectionEnd;
				return !(this.value.length >= max && (keyCode > 50 || keyCode == 32 || keyCode == 0 || keyCode == 13) && !ob.ctrlKey && !ob.altKey && !hasSelection);
			};
			this.onkeyup = function(){
				if(this.value.length > max){
					this.value = this.value.substring(0,max);
				}
			};
		}
	});
};
//use
$('#mytextarea').maxLength(10);
</script>
</body>
</html>